British Prime Minister David Cameron, on an unannounced visit to Afghanistan, said Tuesday he hoped that British troops could start withdrawing next year thanks to inroads against the Taliban.

Cameron's second visit to Afghanistan as prime minister comes days after leaked American diplomatic cables showed heavy criticism by US and Afghan officials of the performance of British forces.

Speaking to reporters at Camp Bastion, the main British base in Helmand province, Cameron said he believed the 2011 date was feasible.

"In terms of the ground being covered, the amount of public being protected, the training of the Afghan National Army that is ahead of schedule, the Helmand police training centre and also the mood of the Paras and Royal Scots that I met -- I think that does give you grounds for cautious optimism that this is going in the right direction," he said.

Cameron left on Sunday for Afghanistan where around 10,000 British troops are stationed -- the second biggest contribution after the United States to the more than 140,000 NATO-led troops fighting a nine-year Taliban insurgency.

Downing Street gave no date for the end of his visit.

He was accompanied by Chief of the Defence Staff General Sir David Richards, who had previously ruled out the prospects of a British withdrawal starting next year.

Asked if he now believed 2011 was realistic, Richards said: "I do.

"It is conditions-based next year but looking at the progress we have made -- I was only here three months ago -- it is quite astronomical how quickly things are coming together."

The last year has seen a massive build-up of US-led forces, trying to drive the Taliban from their strongholds in Kandahar and Helmand provinces as part of a new strategy designed to bring Western troops home as soon as possible.

Mangal was cited in the cables released by Internet whistleblower WikiLeaks as one of the officials criticizing the British.

According to US cables in January 2009, the governor accused the British of doing too little to interact with the local community, instead being holed up in their main base in Sangin district.

President Hamid Karzai was quoted in February 2009 as saying that British incompetence had led to a breakdown in law and order.

And in April 2007, General Dan McNeill, then NATO commander in Afghanistan, was quoted as saying he was "particularly dismayed" by the British who had "made a mess of things in Helmand" owing to the "wrong" tactics.

US Secretary of State Hillary Clinton tried to reassure Britain over its role in Afghanistan last week, expressing "deep respect and admiration for the extraordinary efforts" of British forces in the country.

She said she wanted to express "our regret if anything that was said by anyone suggests to the contrary".

Britain's defense ministry has defended its troops' contribution, and said the situation in Sangin -- responsibility for which was handed over to the United States in September 2010 -- was much improved.

A total of 346 British personnel have died since operations began to topple the Taliban government in October 2001.